Indonesia is scrambling in the wake of two deadly natural disasters occurring back to back in separate regions of the archipelago.
On the island of Java, thousands of villagers are fleeing eruptions from Mount Merapi, Indonesia’s most active volcano. At about the same time, a tsunami, set off by a magnitude 7.7 undersea quake wreaked havoc through the island chains of West Sumatra.
The undersea earthquake west of Pagai Island in the Mentawai archipelago created a tsunami, with initial reports suggesting that the surge reached 10 feet in height and inundated as far as 2000 feet inland. A strange aspect of this event is that the tsunami wave height seems to be much larger and more destructive than the reported earthquake magnitude would suggest.
Indonesia lies along a very tectonically active region of the earth. The west coast of Sumatra and the south coast of Java are at the border between the Eurasian and Australian tectonic plates. The gradual subduction of the Australian plate under the Eurasian plate has caused several natural disasters in the past few years, most notably, the 2004 Indian Ocean Tsunami.
Senior coastal scientist Jose C. Borrero, focusing on tsunami research at ASR limited and University of Southern California, developed tsunami inundation models just hours after the event.
Earthquake magnitude refers the amount of energy released over the course of the event. However, what it does not indicate is the time period over which the energy is released. The length of time over which seismic energy is released can have a profound impact on the resulting tsunami surge.
So called ‘slow’ earthquakes result in more efficient wave generation, leading to a more severe tsunami.
These are the factors that contribute to a quake being not just a normal seismic event and rather what is referred to as a ‘tsunami earthquake.’ The unexpectedly powerful surge from this recent tsunami indicates that it may have been the result of a ‘tsunami earthquake.’
Was the quake that struck off the coast of Sumatra a slow ‘tsunami quake?’ Researchers and scientists are mobilizing to study data and first hand effects of the tsunami are still trying to determine if this is the case.
Dr. Borrero has studied the causes and effects of tsunami in Sumatra some of his published works are listed below.
Borrero, J.C., McAdoo, B., Jaffe, B., Dengler, L., Gelfenbaum, G., Higman, B., Hidayat, R., Moore, A., Kongko, W., Lukijanto, Peters, R., Prasetya, G., Titov, V., Yulianto, E. (in press) Field Survey of the March 28, 2005 Nias-Simeulue Earthquake and Tsunami, Pure and Applied Geophysics
Borrero, J.C., Weiss, R., Okal, E., Hidayat, R., Suranto, Arcas, D., and Titov, V.V., (2009), The Tsunami of September 12, 2007, Bengkulu Province, Sumatra, Indonesia: Post-Tsunami Field Survey and Numerical Modeling, Geophysical Journal International, Vol 178, p. 180–194 doi: 10.1111/j.1365-246X.2008.04058.x
B.G McAdoo, Richardson N., and Borrero J.C. (2007). Inundation distances and run-up measurements from ASTER, QuickBird and SRTM data, Aceh coast, Indonesia. International Journal of Remote Sensing V28, No. 13-14, July 2007.
Borrero, J.C., Sieh, K., Chlieh, M. and Synolakis, C.E. (2006), Tsunami Inundation Modeling for Western Sumatra, Proceedings of the National Academy of Science, V. 103, No. 52, p. 19673 – 19677.
J.C. Borrero, C.E. Synolakis, H.M Fritz (2006) Northern Sumatra Field Survey after the December 2004 Great Sumatra Earthquake and Indian Ocean Tsunami, Earthquake Spectra, V 22, S3, June 2006, S93 – S104.
Bruce E. Jaffe, Jose C. Borrero, Gegar S. Prasetya, Robert Peters, Brian McAdoo, Guy Gelfenbaum, Robert Morton, Peter Ruggiero, Bretwood Higman, Lori Dengler, Rahman Hidayat, Ettiene Kingsley, Widjo Kongko, Lukijanto, Andrew Moore et al. (2006) Northwest Sumatra and Offshore Islands Field Survey after the December 2004 Indian Ocean Tsunami, Earthquake Spectra, V 22, S3, June 2006, S105 – S135.
H.M. Fritz and J.C. Borrero (2006) Somalia Field Survey after the December 2004 Indian Ocean Tsunami, Earthquake Spectra, V 22, S3, June 2006, S219 – S233.
Fritz, H.M., J.C. Borrero, C.E. Synolakis, J.Yoo (2006) 2004 Indian Ocean tsunami flow velocity measurements from survivor videos, Geophysical Research Letters, V 33. 2005
Borrero, J.C. (2005). Field Data and Satellite Imagery of Tsunami Effects in Banda Aceh, Science, V. 308, p. June 10, 2005.
Borrero, J.C. (2005). Field Survey of Northern Sumatra and Banda Aceh, Indonesia after the Tsunami and Earthquake of 26 December 2004, Seismological Research Letters V. 74, No. 3, 309 – 317, May/June 2005.